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Astrophysics

Title:Hybrid Inflation

Abstract: Usually inflation ends either by a slow rolling of the inflaton field, which
gradually becomes faster and faster, or by a first-order phase transition. We
describe a model where inflation ends in a different way, due to a very rapid
rolling (`waterfall') of a scalar field $σ$ triggered by another scalar
field $φ$. This model looks as a hybrid of chaotic inflation and the usual
theory with spontaneous symmetry breaking. Another hybrid model to be discussed
here uses some building blocks from extended inflation (Brans-Dicke theory),
from new inflation (phase transition due to a non-minimal coupling of the
inflaton field to gravity) and from chaotic inflation (the possibility of
inflation beginning at large as well as at small $σ$). In the simplest
version of this scenario inflation ends up by slow rolling, thus avoiding the
big-bubble problem of extended inflation.